1. Field of the Invention
The invention lies in the field of furnace operation. More particularly, it concerns apparatus for indicating true draft of the furnace, which includes a piezometric pressure chamber for providing an average value of atmospheric pressure.
2. Description of the Prior Art
In the operation of furnaces, which are fuel fired, air must be caused to be drawn into the furnace in adequate quantity for burning of the fuel. In a great preponderance of cases, air entry is due to the draft (less than atmospheric pressure) within the furnace.
Regulation of draft is vitally necessary for proper and economical operation of the furnaces which serve a multitude of purposes. Therefore, there must be some means for measurement of furnace draft. It is standard practice to equip each furnace with an instrument known as a "draft gauge", which is, typically, an inclined manometer for measurement of the difference between the pressure inside the furnace at a selected point and atmospheric pressure. But, in windy conditions and, due to wind-induced variations in atmospheric pressure, for various reasons which are well known, it is impossible to accurately use the draft gauges when wind velocity exceeds 10 MPH (14.66 feet/second) and this wind movement velocity is close to the national average. For accuracy, the draft gauge is calibrated in units of 0.01 inch WC as a typical condition.
This invention provides an improved means for determining an average value of atmospheric pressure, against which to measure the differential pressure between the atmosphere and the inside of the furnace.